Well, the name of the forum is ideas, and I for one would love to see a Mutator emulated in software. What an awesome wild and wacky plug-in this could be!
I desperately need a guitar tuner in plug-in format; that would be very cool. Just a simple plug-in with a VU meter.
I'd also love to see PSP tackle a good amp simulator -- something on the level of a Line 6 Pod. Besides Amp Farm (TDM only), the only one I know of is Amplitube (by IK Multimedia) which is good...but PSP can do better!
I'm a huge PSP fan. You guys are awesome and make great stuff at great value.